Fix bug in net::RequestPriority -> HTTP/2 dependency conversion.

This CL also defaults this behavior on (subject to finch override), refactors the finch control to be in line with network stack defaults (== based in io_thread.cc),  and removes the non-default performance bot configuration.

BUG=590225
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Review URL: https://codereview.chromium.org/1779733003

Cr-Commit-Position: refs/heads/master@{#382360}
31 files changed